The surface roughening phenomenon of aluminum foil under variable amplitude stress is examined in order to use the foil as the fatigue gauge to detect the total amount of cyclic stress. It is found that the effect of load history on the surface roughening phenomenon can be observed when the stress amplitude varies simply as in two-level single block loading. However, it is negligible small when the stress amplitude varies many times as in two-level multiple loading. In such a case, the stress evaluated from the surface roughness using the aluminum foil fatigue gauge is represented by (Σσ^α_iN_i/ΣN_i)^1/α with sufficient accuracy, where σ_i, N_i, and a are the stress amplitude, the number of stress cycles of σ_i and the material factor, respectively.

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The surface roughening phenomenon of aluminum foil is examined under variable stress, and the controlling parameter that dominates the roughness is clarified. It is found that constant mean stress does not affect surface roughness. When mean stress varies, however, mean stress causes surface roughening. In such a case, the range-pair counting method is appropriate, and the equivalent stress represented by (Σσ^_iN_i/ΣN_i)^1/α dominates surface roughness, where σ_i and N_i are stress amplitude and the number of stress cycles counted by the range-pair method, and a is a material factor. It is concluded that the fatigue gauge made of aluminum foil can evaluate the equivalent stress with high accuracy.

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The fatigue behaviour of a gas-nitrided Ti-6Al-4V alloy has been studied under rotating bending fatigue test. The results were compared to those of annealed materials on the basis of detailed observations on crack initiation, growth and fracture surfaces. Nitriding was performed using smooth specimens for 4 h and 15 h at 850°C in pure nitrogen gas, and the depths of the nitrided layer obtained were approximately 25 μm and 65 μm, respectively. The fatigue lives of material nitrided for 4 h were shorter than those of annealed material, but the fatigue limit increased. On the other hand, fatigue strength was reduced by nitriding for 15 h. It is concluded that the decrease in fatigue strength of nitrided materials is mainly attributed to inferior crack initiation resistance of the nitrided layer.

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Plane bending fatigue tests were carried out on the notched specimens of fiber glass/epoxy laminates for a wide range of notch-root radii and stress amplitudes. Our attention was focussed on the damaged zone near the notch root of specimens. The process of fatigue damage was studied by measuring the luminance at the limited spot near the notch root. Closer observation by means of a scanning electron microscope revealed that the initiation of microcracks at the notch root was accompanied with the decrease of luminance near the notch root. The experiment shows that the number of cycles to failure is determined by both the maximum elastic stress at the notch root and the notch-root radius. On the basis of the concept of severity at the notch root, the experimental results can be clearly elucidated. Applying the fatigue failure criterion derived here, we can make an accurate estimate of the life for notched specimens of FRP.

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Effects of nonmetallic inclusions, shot peening, the decarburized layer and a small surface pit on automobile suspension spring steels are investigated. The effects of all factors can be evaluated from the viewpoint of Murakami et al.'s fatigue strength prediction equation which predicts the fatigue strength with the Vickers hardness Hv of the matrix, the square root of the projection area of an inclusion √(area), and the stress ratio R. Shot peening influences the fatigue strength through the residual stress, i.e., through the stress ratio and the surface roughness. The decarburized layer has low hardness and its hardness hardly changes with shot peening. A surface pit lowers the fatigue strength through its size √(area). There are two possible fatigue fracture origins due to the hardness variation and residual stress distribution. One is at the surface and the other is at the interior, 300∼400 μm below the surface. The lower bound of a scatter of the fatigue strength of a definite number of specimens can be estimated from the prediction equation with the maximum size of inclusion √(area)_max which is predicted by the statistics of the extremes of inclusions.

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In order to clarify the corrosion fatigue process, rotating bending fatigue tests of heat treated 0.45% C steel smooth specimens were carried out in 3% NaCl solution. The emphasis is to perform successive observations by the plastic replica method. The results showed that corrosion pits are produced at the early stages of cycling, most of which then grow with further cycling until a crack initiates from each corrosion pit. The initiation of corrosion pits from slip bands was observed only in the case when the stress range is relatively large (in the range of stress under which slip bands are produced in air).

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An evaluation of static fatigue crack growth characteristics of glass ceramics was conducted by employing a double cantilever beam specimen with side grooves. As a result, glass ceramics were found to have superior resistance to static fatigue crack propagation than do soda-lime-silica glass. Then, the reasons why glass ceramics have characteristics superior to soda-lime-silica glass were examined from the viewpoints of the reaction rate of glass with water molecules, the difference in process zone sizes and the morphologies of propagating cracks. Also, the effectiveness of the procedure of the delayed fracture test using Vickers indented double cantilever beam specimen with side grooves was indicated.

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Cracks act as the sources of acoustic scattering when they are illuminated by incident ultrasonics. They radiate scattering signals, which carry information on the cracks such as location, orientation, shape, and size. In this paper, the spectrum of the reflected Rayleigh wave from the small fatigue crack is interpreted to provide estimates of crack depth and aspect ratio. The crack is initiated at a Vickers indentation and develops by cyclic cantilevered bending. The approach is based on a theoretical calculation of reflection coefficient by sectioning the half-elliptic crack face into small strips ; the reflection coefficient for each strip has been given by the two-dimensional calculation for an edge crack. This nondestructive technique can measure the crack depth larger than 0.13 mm and the crack closure stress from the spectrum response to static bending stress.

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In the previous papers, the hypersingular integral equation method (HIEM) was shown to be useful for exactly analyzing straight crack problems in the two-dimensional plane. The present paper concerns the application of the HIEM for the solution of the problems with intricate crack shapes. As examples, the stress intensity factors of bent and branched cracks under uniform tension are treated. Even in the case of that the bent part of the crack is extremely short, the accurate numerical results are obtained by selecting a convenient set of collocation points. The calculation shows that the HIEM, in which unknown functions are approximated by using Chebyshev polynomials, gives results of better accuracy compared with the previous method using such as stepped functions.

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The onset of an unstable ductile fracture in a piping system is dependent on the compliance and supporting conditions of the system as well as on material properties, while the influence of such geometrical conditions on the unstable fracture initiation must be elucidated in order to evaluate the stability of a piping system which has a complicated three-dimensional geometry. In this paper, a theoretical aspect of the stability of such a piping system is treated, and a general expression of stability is derived applying the principle of the minimum potential energy. It is shown in the paper that the stability of a piping system can be reduced to that of a piping with a certain compliance and subject to the uniform bending moment. Thus, application of the J-T stability analysis concept to a three-dimensional piping system is enabled. Using the above general expression of stability, two stability equations were also derived for the cases of the piping bent from fixed ends and that under 3-point bending with a compliance at the loading point respectively. Furthermore the critical span length of uniformly bent pipe is also calculated for stainless steel and carbon steel pipes using the evaluation procedure described in the paper and the empirical relationships which were presented in previous papers by the author.

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A concept of crack closure pressure is proposed for evaluating tectonic stresses by the hydraulic fracturing stress measurement technique, based on the linear theory of elasticity and the linear fracture mechanics. The crack closure pressure is defined as a pressure value at a turning point appearing in the decrease rate of the downhole pressure vs the downhole pressure curve after the complete closure of the pressurizing circuit for hydraulic fracturing, i.e., shut-in. This is interpreted as a pressure at the instant when the crack which was induced by the hydraulic fracturing on the surface of a borehole closes completely after the shut-in. The relationship between the crack closure pressure and the tectonic stresses is very simple, and no material constants, such as the fracture toughness and hydraulic properties of the rock, appear in the relationship. Thus, it can be applied as a new and extremely useful formula for evaluating tectonic stresses by the hydraulic fracturing tectonic stress measurement technique.

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The characterization for the crack growth rate and the progressive damage region around the crack tip of SUS 304 stainless steel were investigated with various holding times at the maximum stress in a trapozoidal wave in a vacuum at 680°C. From these experimental results, the crack growth rate approaches the creep crack growth rate, and the geometry of the progressive damage region around the crack tip becomes similar with the increase of stress holding time. The fracture surface shows intergranular features dominated by creep in the case of with stress holding time, but does not show without stress holding time. This is distinguished from a triangular wave with no stress holding time, where the fracture implicitly involves fatigue and creep effects.

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The stress intensity factors of a radial edge crack emanating from a circular hole have been analyzed when an infinite plate is step-functionally heated in a circular region near the hole. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the heat source in an infinite plate with a circular hole. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a uniformly distributed heat source and a small crack. The effects of the location of the heat source on the variations of stress intensity factors are considered.

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Fatigue crack growth rates in a residual stress field can be predicted by using a superposition technique. This approach needs an analysis of residual and contact stress intensity factors as the authors proposed in previous papers. Objectives of this study are to discuss an approach for predicting the fatigue crack growth rates near the threshold where the oxide induced crack closure is dominant and to evaluate experimentally an effect of the residual plastic stretch on the crack surface contact. It is concluded that this approach gives a good prediction by the using upper bound of base metal crack growth rate data, and the residual plastic stretch has an effect on the crack surface contact stress.

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This paper purports to study the fracture criterion of a mixed-mode crack and to demonstrate that the criterion based on the CED (crack energy density) is available from completely elastic fracture to elastic-plastic fracture in a unified way. The CED in an arbitrary direction, ε_ψ, is defined as the quantity which has the meaning of strain energy area density in the plane containing a crack front line without any restrictions on the constitutive equation. We may expect that a mixed-mode Crack begins to grow in the direction ψ where ε^I_ψ (the mode I contribution of ε_ψ) takes the maximum value, ε^I_<ψmax> when ε^I_<ψmax> reaches a critical value peculiar to a material (we call this criterion the ε^I_<ψmax> criterion). First, the applicability of this ε^I_<ψmax> Criterion to elastic fracture is shown through the Comparison between the results of the ε^I_<ψmax> criterion and the results of other criteria and experiments. Subsequently, fracture experiments of specimens of aluminum alloy with a crack inclined to the loading axis are carried out, and it is demonstrated that not only fractures with a relatively small yielding region but also fractures with a large yielding region can be explained by this ε^I_<ψmax> criterion.

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A computer-aided analyzing methed was developed for determining the fracture toughness of rock by means of ISRM methods. Fracture toughness tests were conducted on Westerly granite using the short-rod (SR) specimens, and the results were evaluated, utilizing the program. A comparison indicated that the fracture toughness value determined by the computer-aided system agrees well with that obtained from handwork. Based on the crack growth resistance curve, the fracture toughness considering its nonlinearity was successfully determined.

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Mixed-mode (mode I and mode II) interlaminar fracture toughness of unidirectionally reinforced and woven CFRP (Carbon Fiber Reinforced Plastic) is evaluated using DCB (double cantilever beam) specimens. A new testing apparatus is made in order to change the ratio of mode I to mode II in wide range. The fracture toughness value is evaluated based on beam theory, and the deformation of specimens is analyzed by the finite element method. The relation between compliance and clack length obtained by experiment agrees with the results obtained by FEM. The constant fracture toughness value, G_C, which is independent of crack length, is obtained. Due to the decrease of the G_I/G_II ratio, the fracture toughness value increases. It is shown that the role of mode II changes largely due to the change of the ratio of mode I to mode II, though the mode I component keeps a nearly constant value.

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Three-dimensional elastic-plastic analyses were carried out on 1 and 2 mm-thick CCT specimens with or without side grooves. The valid effective thickness, 0.85√(B_O·B_N), was obtained from the 3-D analyses. The stretched-zone method is better than the R-curve method to determine the J_in value of the thin specimen. However, a great many data should be gathered near the J_in value. The J_in value obtained using side-grooved specimens is always lower than that of non-side-grooved specimens. Considering the difficulty of machining the side groove, the side groove is not appropriate for the thin specimen. As the thickness decreases, the J_in value decreases. However, it is possible to estimate the J_IC value from the J_in value obtained using thin CCT specimens.

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In order to examine hydrostatic stress effects on the fracture strength of brittle material subjected to multiaxial stress states, glass ceramic specimens with an indentation-induced flaw were tested by four point bending under both atmospheric and hydrostatic pressures of up to about 100 MPa. The tests were conducted under both low and high stressing rates to provide data for different conditions of subcritical crack growth for the respective cases. The maximum tensile stress at fracture clearly increased with hydrostatic pressure in high stressing rate tests, though little significant difference was observed in strengths in low stressing rate tests. Such increase in fracture strength under high stressing rate conditions was attributed to the fact that the subcritical crack growth in region III which depend on the crack tip structure in the glass ceramics would be restricted by hydrostatic pressure ; because of this, a wide cohesive region at the crack tip favors abrupt fracture.

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Ultrasonic testing using a normal incident longitudinal wave is treated for sizing a closed crack. The crack exists vertically on the back wall of a plate inspected. Reflection and transmission of the wave at the closed crack surfaces are analysed by introducing a model of crack closure. The model includes a stress closing the crack and a phase shift of the reflected and trasmitted waves as unknown parameters. The unknown parameters have been determined together with the unknown length of the crack by analysing the inverse problem, which compares the back-wall echo height obtained through both theory and experiment. Two kinds of cracks introduced by different stress ratio in fatigue have been examined. The ultrasonic measurements for specimens have shown that the present analysis offers a powerful tool for precise sizing of closed vertical crack.

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Boundary value inverse problems deal with the estimation of unknown boundary values on incompletely prescribed boundaries using over-prescribed boundary values on other boundaries or in the domain. Like many other inverse problems, this kind of inverse problem is usually ill-conditioned. In the present paper, a regularization scheme was proposed for solving the ill-conditioned boundary value inverse problems. The scheme was based on a multivariable constrained optimization algorithm for determining the most plausible solution satisfying inequality constraints deduced from information on unknown variables available in advance. To demonstrate the applicability of the proposed scheme, it was applied to a boundary value inverse problem with trusslike structures. The nonpositiveness or nonnegativeness of unknown variables was used as the constraint. It was found that the scheme using the constraint was effective in obtaining reasonable estimates of the unknown boundary values and was rather insensitive to error in input data, while the unconstrained scheme was not.

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A numerical study is made of the transient, uncoupled dynamic thermal stresses in spherical and cylindrical bodies subjected to arbitrarily prescribed symmetric temperature fields. The numerical procedure employs appropriate characteristic relations on boundaries and on interfaces between media with different material properties while using more convenient explicit finite difference approximations at all other points. The solutions of the specific examples calculated show excellent agreement with existing solutions by other methods. Numerical examples are also given for the stress wave propagation in composite hollow spheres and circular cylinders subjected to step heating on the inner boundary.

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The thermal stress in silicon chips encapsulated in IC plastic packages under temperature cycling was discussed. Stress-sensing chips utilizing the piezoresistive effect were used for the stress measurement. It was found that the chip stress increased gradually with increase of the number of temperature cycles between -55°C and 150°C. The reason for this increase of the chip stress was explained by considering viscoelastic phenomena of the resin material used for the encapsulation of packages. When the holding time at 150°C was shorter than the stress relaxation time of the resin at that temperature, this stress increase was observed. It was found analytically that this stress increase could be more than 10% when the holding time was much shorter than the stress relaxation time of the resin.

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The creep characteristics of Ni-NiO dispersion-strengthened alloy and pure nickel as a reference material have been examined in the temperature range of 873-1123 K and in the stress range of 21-73MPa. Structural changes during creep were studied using transmission electron microscopy. Marked differences in sabstructure and creep behavior were found between Ni-NiO alloy and pure nickel. The results obtained are as follows : (1) The value of α, which is the important parameter in evaluating an effective diffusion coefficient Deff, for Ni-NiO alloy was smaller than that for pure nickel. This is caused by low dislocation density in Ni-NiO alloy. (2) The dominant creep deformation mechanism for both materials is a dislocation creep which is controlled by climb of dislocations. (3) Slender and curved subgrains were observed in Ni-NiO alloy. It is suggested that nickel oxide particles act as obstacles to subboundary migration.

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This paper presents some results of transient heat-transfer and thermal-stress analyses of functionally gradient materials (FGMs) subject to rapid heating. The objective of this study is to examine the effect of changing compositional distribution profiles in FGMs on the transient thermal stresses. Finite-element analysis are conducted on FGMs which posess different compositional gradients with varying mixture ratios of ZrO₂ and NiCrAIY deposited on a copper substrfte. The thermal boundary conditions used for the analysis simulate the thermal load encountered in the thrust chamber of a rocket engine. A two-dimensional, axisymmetric model is used for the numerical computations, where the outer ZrO₂ surface is subject to a heat flux and the inner copper surface temperature is kept at 0°C. It is shown that the hoop and axial stress in the FGMs are compressive, and the maximum tensile stress is the radial direction is induced at the interface between the coating layer and substrate, regardless of the different compositional profiles. It is further demonstrated that the gradient composition cas mitigate both the in-plane compressive stresses and interfacial radial tensile stress which are responsible for the cracking and delamination of the coating layers.

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Friction and wear of contact surfaces during rolling and sliding should be predicted precisely and then controlled well to develop hightechnology in the industry. In order to alalyze the cyclic plastic deformation in the repeated rolling-sliding contact, it is necessary to use the constitutive model for cyclic plasticity. However, there is no analysis in repeated rolling-sliding contact using the constitutive model. Recently, the first author proposed a constitutive model for metallic material subjected to cyclic loading assuming strain hysteresis dependency, using the loading function considered as the motion of the center of the loading surface. In this paper, an attempt is made to analyze the behavior of the inelastic deformation of S20C during rolling and sliding under a contact pressure sufficient to cause yielding, using a finite element method incorporated in the constitutive model. As a result, it is demonstrated that this model is effective for this kind of problem.

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The elastic problem for thick-walled tubes of a functionally gradient material (FGM) under internal pressure in the case of plane strain (ε_z=0) has been studied. The model components of FGM are based on the combination of the matrix having three kinds of elastic moduli of 35, 70 and 210 GPa, and the powder having an elastic modulus of 360 GPa. The distribution profile is assumed by the expressions reported previously for the corundum/plaster FGM. The elastic stress and strain distributions for FGM become complicated because of radial elastic modulus gradients. The effects of distribution profiles on the deformation can be summarized by considering the variation of the normalized elastic modulus gradient [(dE/dr)/E] in the radial direction. If a greater positive normalized elastic modulus gradient is obtained, the circumferential stress at an inner surface of a tube is decreased, and then the tube begins to function as a compound tube.

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In this paper, the load distribution effect of sheet plate that is put on the fundamental parts subjected to a load is analyzed by using the finite-element method. In the analyses, the thickness and material property of the sheet plate and the composition of fundamental parts are changed. Moreover, the sheet plates composed of several materials are analyzed. The load influence factor R between the sheet plate and the fundamental part is defined and the values for several models are calculated. By using the factor R, the theoretical technique estimating the load distribution effect is proposed. The technique is applied to the practical system measuring contact pressure distribution and the load distribution effect is discussed.

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Design variable reduction is a very important technique for obtaining efficient structural optimization using a mathematical programming technique. Two reduction techniques based on the isoparametric interpolation method and the trigonometic series interpolation method are suggested. The minimum compliance design problem subjected to volume constraint and its sensitivity analysis are formulated for these reduction techniques, based on the boundary element analysis. These techniques concatenated with the sequential quadratic programming method are applied to determine hole shapes in the plates under biaxial uniform loading with different stress ratios and a shape of a multiconnected cantilever structure. From these numerical results, the validity and applicability of the reduction techniques are confirmed.

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A BEM analysis system (BEM-LAM) of composite laminates with emphasis on accuracy and efficiency is developed. This system can analyze two-dimensional laminates for both isotropic and orthotropic layers under a plane strain state. Accuracy studies show that BEM-LAM using a subelement division scheme in quasi-singular integral gives very accurate solutions even if the layer aspect ratio is equal to thousands. In this study, the BEM-LAM is applied to analyze the problems of shear deformation, free-edge effects and multilayer structures. Accurate solutions are obtained which satisfy exactly the boundary conditions as well as continuity of traction and displacement on the interface between layers. This system could be applied to optimal design problems of laminate materials.

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Stress intensity factors for load-controlled C-shaped specimens (LC-CSS) are discussed in some literatures, but those for displacement-controlled C-shaped specimens (DC-CSS), which are often used for environmental fracture toughness testing, are not. In this paper, an analytical procedure is shown by which to estimate mixed-mode stress intensity factors for DC-CSS with some internal and external axial cracks. The results obtained are summarized as follows : (1) Analytical results for LC-CSS show good agreement with the numerical data in the literature. (2) Mode II stress intensity factors are always negligible as compared to mode I stress intensity factors for commonly used thin-walled rings. (3) Explicit formulation of the stress intensity factors obtained in this paper is effective for both practical use and the discussion of influential parameters. (4) Several parameter studies for DC-CSS show that it is important for the analysis of such statically indeterminate structures to consider the variation of the system's compliance due to the presence of cracks.

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The rapid heating and cooling and the volume expansion due to the martensitic transformation in partial induction-hardening of steels will induce the strong residual stress which strongly affects the strenght of steels. Cylindrical steel specimens of JIS type S45C were partially induction-hardened and tempered at various temperatures. The residual stress distribution and the Gaussian curve parameter (GCP) representing the X-ray diffraction line broadening were determined by X-rays. A quenched specimen had a high compressive residual stress of approximately 1000 MPa, GCP of 5degree, and Vickers hardness of 800; these values decreased with increasing tempering temperature. The residual stress almost vanished at 773 K and the GCP did not change greatly above this temperature, but the hardness decreased up to 1083 K. The Vickers hardeness H_V of quenched and tempered steels can be nondestructively evaluated from GCP a by H_V=330√(α-0.5)+137C+35, where C is the carbon content (%) of steels.

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The Cosserat continuum theory or theory of polar materials is intended to reflect the effects of microscopic structure in the macroscopic behavior of materials. These theories are intimately related with the notion of nonlocality at a single point. In contrast with the mechanical nonlocal effects in these theories, in this paper, thermodynamical nonlocality is taken into consideration. The entropy production rate presented here is affected by the fluctuations of temperature, radiation and heat fulx vecter, which do not appear in the condition of local equilibrium. By averaging the microscopic quantities, macroscopic variables which express the nonequilibrium condition can be obtained. The first law of thermodynamics in this study has the same form as for a thermal simple body. However, the form of the second law is modified by the above fluctuations and the secondary moment of microvolume. Through these equations, we may expect to construct constitutive equations which may include the effects of strong nonequilibrium conditions.

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The Cosserat continuum theory or theory of polar materials intends to reflect thhe effects of microscopic structures into the macroscopic behavior of materials. In contrast with the effects of mechanical microstructures of these theories, in this paper, thermodynamical microstructures are taken into consideration. A previous report called these materials "thermopolar materials". The Clausius-Duhem inequality is intoduced, including the terms of the temperature gradient. Using this inequality, constitutive equations are obtained, and it is made clear that the values of stresses or thermodynamical quantities under nonequilibrium condition; are different from the values under local equilibrium conditions. Also, in the constitutive equation for stress, "temperature gradient stress" of a positive value is introduced.

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In order to investigate the impact characteristics of friction welded joint, the instrumented Charpy impact tests have been carried out at various temperatures from 77 K to 473 K, using 0.46 %C carbon steel specimens with butt joint. The main results obtained are as follows : (1) The impact value of the weld interface at the room temperature is apporoximately 30 % lower and at the upper shelf nearly 50 % lower than that of the parent material. (2) The deformation and crack propagation energy in the weld interface over the room temperature is remarkably small in comparison with that of the parent material. (3) Both the energy and fracture appearance transition temperature of the weld interface are higher than the transition temperatures of the parent material and the room temperature. (4) The absorption energy at the heat affected zone is in all regions extremely larger than absorbed energy of the parent material. The transition temperature is the lowest. (5) The impact bending strength is in the order of the heat affected zone, weld interface and parent material, regardless of the test temperature, but these strengths become the maximum around the highest temperature, where 100 % brittle fracture occur.

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In this paper the characteristics of the stress fields near a corner of jointed dissimilar materials under antiplane loads are studied. It is found that the singular stress fields due to the antiplane loads can be divided into two types: a symmetric type with a stress singularity of 1/γ^1-λ₁ and a skew-symmetric type with a stress singularity of 1/γ^1-λ₂. If G₂<G₁, there exists only the singularity of skew-symmetric type, and if G₂>G₁, there exists only the singularity of symmetric type. An expression of stress fields at the close vicinity of the corner is presented. Based on the expression the singular stress fields are defined in terms of two constants K_{III, λ1} and K_{III, λ2} for the symmetric type and the skew-symmetric type, respectively.

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The stress field near the corner of an inclusion has singularities. For the mode I deformation, the stress singularity is 1/γ^1-λ₁, and for the mode II deformation, it is 1/γ^1-λ₂. Thus, the stress fields around the singular point must be described in terms of two pairs of constants: λ₁, K_{I, λ1} and λ₂, K_II.λ2, where K_{I, λ1}, and K_II.λ2 are the parameters representing the intensity of the stress field. In this study, the body force method is used for calculating K_I.λ1 and K_II.λ2 in the problem of an infinite plate with an inclusion. In the numerical analyses, the singularity of the stress field at the corner tip is taken into account by introducing new basic density functions of the body forces.

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In this paper, the singular stress fields near a corner of jointed dissimilar materials are discussed based on the expressions of the stress fields obtained recently by the authors. The stress fields are expressed as a sum of two terms: a symmetric term and a skew-symmetric term. The stress singularities for the two terms are different. The angle where the normal stress σ_θ or the shear stress τ_γθ becomes the maximum is a function of the distance from the corner point, differing from the case of a crack.

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By using the theoretical results for closed-form analytical solutions of in-plane problems inclusion under point forces, dislocations and so on, several numerical examples are shown by many graphical representations. The previous results published by several authors can be included as particular cases of our solutions.

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The Laplace transformation is known as one of the most powerful mathematical techniques for solving wide range of problems in engineering. For its application to practical problems, many authors have extensively studied methods of numerical inversion. On the other hand, the method of numerical transformation has not been studied very much. For this reason, most of the applications were limited to theoretical or numerical analysis and there were few applications to experimental analysis. To overcome this problem, both of the numerical transformation and inversion are studied in this paper. Numerical accuracy is evaluated and discussed using two test functions, sinusoidal and step function. A chart is presented for determining the parameters of computation under a specified accuracy.

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Microdynamics of chevron-notched isotropic carbon were investigated by the source inversion processing of elastic waves. The geometric correction factor for stress intensity factor Y determined by compliance measurement was found to agree well with that or the superpose method by D. Munz. The fracture toughness of this material was 1.3MPa·m^1/2. The AE monitoring system (ADAS) developed by the authors was demonstrated to measure the surface displacement generated by mode-I cracking. Therefore, the source waves, crack volume and released energy were obtained by the time-domain deconvolution integral of detected displacement by the theoretical Green's function of the media. The area produced by stable crack propagation was found to be about 0.5-1.0mm², and to agree fairly well with the characteristic features of the fracture surface. The stable crack growth velocity was estimated to be about 250m/s.

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In the present paper, the proof testing effects were discussed when the temperature conditions of the proof testing are different from those of actual loading. The experiments were conducted on sintered Si₃N₄ specimens under 4-point bending in the fast fracture mode. The 1000°C strength distribution of sintered Si₃N₄ which had been proof tested at room temperature was compared with that of the virgin material. It was shown that the proof testing conducted at room temperature improved the strength distribution of the material at 1000°C. Though the strength distribution of the proof tested material did not exactly coincide with the theoretically predicted one, the discrepancy may be attributed to the statistical divergence caused from small sample size. So, it was concluded that the proof testing remains effective even if there exists a temperature difference between proof testing and actual loading.

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A pulsed laser-atom probe has been used to investigate microstructural change and phase separations that occur during 475°C embrittlement of ferritic stainless steel. In this study the Fe-28% Cr-5%Ni alloy was aged at 450°C for as long as 5000h. In addition to the atom probe analysis, hardness, the fatigue crack propagation rate and Charpy V-notch impact-energy absorption were measured. We have found that the amplitude of the initial Cr concentration fluctuation increases with ageing up to 1035h and the alloy aged at 450°C undergoes a spinodal decomposition. The size of Cr-rich precipitates increases with ageing time up to 5000h, while the wave length is saturated to 18∼32A^^○ at the ageing time of 1035h. The Cr-rich phase formed is considered as the major factor for the embrittlement.

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Atmospheric corrosion of thin-film cobalt-based magnetic recording media was studied by surface analysis and by the experimental deposition of dummy particles. Thin-film corrosion tends to be affected by dust particles that adhere to the surface, even in a clean environment. The incidence of corrosion depends on the size of the dust particles. Surface corrosion is more conspicuous away from adherent dust rather than directly under it. Corrosion in those areas involves water adsorption through a porous overcoat, cobalt dissolution from the magnetic layer, and migration of cobalt ions through the carbon overcoat. We propose the following thin-film corrosion model; atmospheric vapor condenses in the crevice between the carbon overcoat and the dust ; this water penetrates and diffuses into the carbon overcoat, and a differential aeration cell is generated by the difference in dissolved oxygen concentration between the edge and center of the areas with diffused water. Furthermore, we propose a corrosion test method for thin-film recording media using uniform particles.

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To study the mechanical properties of the human knee joint and its removal, artificial tibial components have been investigated by a visco-elastic spectrometer and a testing machine of the Instron type. Damage of artificial tibial components was measured by stereological pattern analysis and a roughness meter. At the upper tibia in cancellous bone, the average compressive strength of the medial part was 7.6 MPa and that of the lateral part was 5.1 MPa. At the damaged artificial tibial components, comparing lateral and medial sides, we find that the lateral side is damaged more than the medial side.

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In this paper, the method of analyzing a two-dimensional stationary thermoelastic problem based on the body force method (BFM) was studied. BFM is known as a highly accurate boundary type method for isothermal elastic problems, but this method has not been extended to analysis of a thermo elastic problem until now. In order to show the effectiveness of the present method, thermoelastic problems were solved for a uniform heat flow disturbed by an insulated hole or an insulated crack.

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Fracture toughness tests were performed in the ductile-brittle transition temperature region using 65 three-point bend specimens which were cut out from SM41C carbon steel. Consideration of the probabilistic characteristics of fracture toughness, the crack initiation point of the brittle fracture and the plane strain condition gives the following results. (1) The probability distribution of fracture toughness shows the Weibull distribution. (2) The area of the plane strain condition is estimated from the crack initiation point and the shape of the crack front of the fibrous ductile fracture. The following equation giving the condition for plane strain in the center of the thickness is proposed : B≥0.0037{K_c(J)/σ_ys}²+0.0092. (3) The thickness effect of the brittle fracture toughness is caused by the probability distribution of the weakest point in the crack front, namely, the Weibulltic volume effect.

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A continuous wave, YAG laser was employed to perform the heat treatment of the surface of precracked specimens, and rotational-bending fatigue tests have been conducted on laser-treated specimens. The results obtained are summarized as follows: (1)Laser surface treatment has a beneficial effect of increasing the fatigue strength of a steel specimen with the crack shallower than the surface hardening depth. (2)A small fatigue crack at the specimen surface which has been laser treated is still closed even under application of static tensile stress equal to the fatigue limit of the specimen. This suggests that crack closure is a dominant controlling factor of the nonpropagation of a fatigue crack in the laser treated area.

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In a vehicle design to realize good crash properties, it is desired to increase the maximum and the mean crash load of a vehicle structure. A sensitivity analysis may be used to examine a vehicle structure efficiently. However, no report regarding this usage has been presented because of complex nature of a vehicle crash analysis. In this paper, a new method for a sensitivity analysis is presented, which deals with a bucking load directly. As the first report, sensitivity of a structure to increase dynamic buckling strength is investigated, where the dynamic buckling is regarded as higher order static bucking whose mode is similar to the dynamic mode. A new approach to dynamic buckling problems based on a study of dynamic properties is introduced and discussed.

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An experimental method of direct comparison of surface roughening after plastic deformation and deformation of grains is developed. The shape of the free surface after plastic deformation is measured with a stylus measuring instrument and the data is put into a personal computer. A new experimental technique to compose a precise 3-dimensional pattern of the surface is developed in the present paper. The pattern of grain boundaries observed by a microscope is also recorded in the computer and both figures are superimposed on the display. Some experiments are performed on the compressive deformation of polycrystalline iron and discussion is presented on the relationship between surface roughening and deformation of grains.

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